Synthetic lubricants containing phosphorothionates and arylamines



United States Patent Oflice Patented it-3,211,:

which contains minor amounts of a triaryl ester of phosphorothionic acid as hereinafter defined, an arylamine 3,429,813 and/ or a thiodiarylamine. SYNTHETIC LUBRICANT CONTA N N PHOS- Suitable triaryl esters of phosphorothionic acid contain PHOROTHIONATES AND ARYLAMINES from six to about fourteen carbon atoms per aryl group.

Francis H. Waight, Eastham, Win-a1, and Alexander c. B. 5 MacPhail, Little Sutton, Wirral, England, assignors to Shell Oil Company, New York, N.Y., a corporation Examples of triaryl esters are triphenyl, tritolyl, tribenzyl, trixylyl, naphthyldiphenyl trinaphthyl, and triof Delaware octyl phenyl phosphorothionates, An especially preferred No Drawing. Filed Sept. 23, 1964, Ser. No. 398,742 ester is triphenyl phosphorothionate, The triaryl esters of Claims priority, application Great Britain, Oct. 25, 1963, the invention may be used in concentrations between 42,137/63 about 0.5% and 10% by weight, preferably between us 252-465 9 Claims 2 and 7% by weight based on the final lubricating oil. C1091 3/42 Suitable arylamines and thiodiarylamines are described in Mehr et al., US. 2,815,327, issued Dec. 3, 1957. Examples of appropriate arylamines are diphenylamine,

phenyl-u-naphthylamine, phenyl-fi-naphthylamine, a,oc'-

dimethylamine, methyl phenyl-a-naphthlamine, phenyl-fi- (butylnaphthyl)amine, and a,;8-dinaphthylamine. Diarylamines are preferred. Appropriate thiodiarylamines are phenothiazine, phenylthio-a-naphthylamine, a,a'-thi0dinaphthylamine, and 3,7-dioctyl phenothiazine. In general, for both additive the aryl nuclei are phenyl or naphthyl and may be alkylated with up to four alkyl groups having from one to ten carbon atoms. The amine additives are advantageously used in concentrations of about 0.5% to 5% by weight, preferably 1 to 3% by weight based on the final compositon. In an especially preferred aspect of the invention, the triarylphosphorothionate is used in combination with both an arylamine and a thiodiarylamine as defined above.

This invention relates to improved synthetic lubricating compositions which are oxidation-stable and which have excellent anti-wear properties. In a preferred aspect the invention relates to improved aircraft turbine lubricants which contain certain esters of phosphorothionic acid in combination with certain amine antioxidants.

Synthetic lubricants have recently gained prominence in the field of lubrication because they are able to meet the more stringent requirements of certain new applications. They have found use in jet aircraft where wide temperature ranges and extreme operating conditions are likely to be encountered. Under these extreme conditions, synthetic oils are often corrosive and undergo thermal and oxidative deterioration resulting in sludge and deposit formation, viscosity change, discoloration and other undesirable changes. Attempts to correct these deficiencies by conventional methods are frequently unsat- To illhstrate the Surprising eoeetion 0f the additives isfactory because of the extreme nature of the applicaof the lhvenhoh, Several repfesentahve COIIIPOSIUOIIS tion of the oil. For example, addition of a conventional f fhfmuleted and f the l hy BIQWII antioxidant to reduce deterioration may cause increased QXldatwn Test, wherelh ahtl?xldaht hf y 15 expfessed corrosion, or addition of an antiwear agent might dem terms of changes of VISCOSIIY and y- Referl'lhg to crease stability. Furthermore, the addition of more than Table formhlatlons I through VIII y {nade Wlth one additive frequently compounds the problem because one Of the ep Components 0f the lnvenhon absentof incompatibility of the additives. Therefore, although These hlhfleahts Were tested agelnst formhlehons IX a particular additive might aid oxidation stability, the 40 through Which Were compounded accfn'dlhg to the further addition of a known extreme-pressure agent is invention. All Compositions were tested In e Rolls likely to detract from the effectiveness of the antioxidant. Royce OXidatiOn Test. In this test, 250 P mlhhte of It has now been found that certain triarly esters of air nitrogen Saturated With Water Vapor bubbled phosphorothionic acid are excellent extreme-pressure under controlled Conditions through a boll Sample agents and cooperate with certain known amine antiat 220 C. for 192 hours. The deterioration of the oxidants to markedly improve oxidation resistance of lubricating oil due to oxidation is then measured in terms certain synthetic ester lubricants. Accordingly, the invenof acidity and viscosity changes and benzene insolubles. tion provides an improved ester-based synthetic lubricant The results of these tests are reported in Table II.

TABLE I Composition 0! Example (percent wt.) I II III IV V VI VII VIII IX X XI XII XIII XIV Trimethylol propane tripelargonate 63.0 61.0 94.98 75.98 60.0 58.0 58.0 58.0 91.98 72.98 53.0

Hercolube A" (0 43 acid esters of pentaerythritol) 19.5 19.5 19.5 94. 98 19.5 19.5 19.5 19.5 91.98 19.5 19.5 HerfoIube (3" (04-01 acid esters of pentaerythrito Herizflube F (Cr-C acid esters of dipentaeythri- Bis(2,2,4-trimethylpentyl)azelate-.- Phenyl-a-naphthylamine 3,7-dioctyl phenothiazine.-. Triphenyl phosphorothionate. Aroclor 1254 (chlorinated dipheny 5-methyl benzotriazole (p.p.m.) AutioxidantA 1 2.0 Anti0xidantB" 1 2.0 D.C. 200/12500 silicone (p.p.m.)- 5 5 5 5 5 5 5 5 5 5 5 5 5 Azelaic acid 0. 02 0. 02 0. 02 0. 02 0. 02 0.02 0. 02 0. 02 0. 02 0. 02 0. 02 O. 02 0. 02 0. 0

l a,a',a-(2,4,fi-trimethyl-1,3,5-benzenetriy1)tris-(2,6-ditertiarybutyl pcresol). 9 4,4'-(2,3,5,G-tetramethylxylyleue)bis-(2,6-ditertiarybutyl p-cresol).

TABLE II Benzene Viscosity at 210 F. (05.) Acid Value Insolubles (mg.KOH/g.) Composition (percent wt.) Initial Final Percent Initial Final Increase Example I Solid II Solid III Solid IV Solid V Solid O. 017 27. 8 446 6. 55 VII 5. 08 0. 10

0. 012 32. 6 547 6. VIII 5. 04 0. 10

I111 11. 9 148 4. 90 IX 4. 8O 0. 10

0. 004 13. 6 172 4. 80 XII 5. 00 0. l0

0. 006 11. 7 132 8. 75 XIII 5. 04 0. 10

O. 05 9. 43 72. 5 4. 60 XIV 5. 47 0. 20

Table II shows that the use of a triaryl ester of phosphorothionic acid imparts essentially no antioxidant activity when used alone in a synthetic ester lubricating oil (Examples I-V). Examples IX-XIV evidence the enhanced antioxidant activity imparted by the triaryl esters to the known amine antioxidants. This increase is shown by the reduction in benzene insolubles, viscosity increase, and acid value resulting from the addition of the phosphorothionate .to the amine-containing oil. The increase in antioxidant activity is indeed even greater than that attributable to other well known antioxidants used in combination with an aryl amine and a thiodiarylamine (Examples VII and VIII).

The phosphorothionie acid esters can be prepared in any manner known to the art. For example, thiophosphoryl chloride can be prepared from sulfur and phosphorous trichloride and can subsequently be reacted with the appropriate phenol in the presence of a Friedel-Crafts catalyst such as aluminum chloride. Alternately, phosphorus trichloride can be added at temperatures of from about 50 to 150 C. to a mixture of elemental sulfur with an appropriate phenol to yield the desired ester in a onestep process.

Although the additive combination of the invention is generally applicable to both synthetic and mineral lubricating oils, it is particularly desirable for use in synthetic oils. Synthetic ester lubricants are especially preferred.

Preferred synthetic lubricant base stocks are esters of alcohols having 1 to 20, especially 4 to 12, carbon atoms and aliphatic carboxylic acids having from 3 to 20, especially 4 to 12, carbon atoms. The ester base may be a simple ester (reaction product of a monohydroxy alcohol and a monocarboxylic acid), a polyester (reaction product of an alcohol and an acid, one of which has more than one functional group, or a complex ester (reaction product of a polyfunctional acid with more than one alcohol, or of a polyfunctional alcohol with more than one acid). Also, excellent synthetic lubricants may be formulated from mixtures of esters, such as major proportions of complex esters and minor amounts of diesters.

Monohydric alcohols suitable for making ester -base stocks include methyl, butyl, isooctyl, dodecyl and octadecyl alcohols. 0x0 alcohols prepared by the reaction of olefins with carbon monoxide and hydrogen are suitable. Neo alcohols, i.e., alcohols having no hydrogens on the beta carbon atom are preferred. Examples of such alcohols are 2,2,4-trimethylpentanol-1 and 2,2-dimethyl propanol.

Polyalcohols used for the production of base oil esters preferably contain 1 to 12 carbons. Examples, of dialcohols are 2-ethyl-1,3-hexanediol, 2-propyl-3,3-heptanediol, 2-butyl-l,3-butanediol, 2,4-dimesityl-1,3-butanedi- 01, and polypropylene glycols having molecular weights from about 100 to 300. Alcohols having three, four, five or more hydroxyl groups per molecule are also suitable and are preferred; examples of these polyols are pentaerythritol, dipentaerythritol, and trimethylolpropane. Mixtures of alcohols may also be used.

Suitable carboxylic acids for making the ester base oils include monoand dibasic aliphatic carboxylic acids. Examples of appropriate acids are butyric, valeric, sebacic, azelaic, suberic, caproic, adipic, ethyl suberic, glutaric, pentadecanedicarboxylic, thiodiglycolic, proprionic, caprylic, pimelic, and mixtures thereof. Preferred acids are se'bacic, azelaic, glutaric, adipic, and their mixtures.

Examples of suitable ester base oils are ethyl palmitate, ethyl laurate, butyl stearate, di(2-ethylhexyl) sebacate, di-(2-ethylhexyl) azelate, ethyl glycol dilaurate, di-(2- ethylhexyl) phthalate, di-(1,3-methylbutyl) adipate, di- (l-ethylpropyl) azelate, diisopropyloxylate, dicyclohexyl sebacate, glycerol tri-n-heptoate, di(undecyl)' azelate, and tetraethylene glycol di-(2-ethylene caproate), and ,mix' tures thereof. A preferred mixture of esters consists of about 50 to wt. bis(2,2,4-trimethylpentyl) azelate and 20 to 50% wt. 1,1,1-trimethylyl propane triheptanoate.

Especially preferred esters for use as base stocks in the present invention are esters of monocarboxylic acids having three to twelve carbons and polyalcohols such as pentaerythn'tol, dipentaerythritol, and trimethylolpropane. Examples of these esters are pentaerythrityl tetra-butyrate, pentaerythrityl tetracaproate, pentaerythrityl dibutyratedicaproate, pentaerythrityl butyratecaproate divalerate, pentaerythrityl butyrate trivalerate, pentaerythrityl tributyratecaproate, mixed C saturated fatty acid esters of pentaerythritol, dipentaerythrityl hexavalerate, dipentaerythrityl hexaheptoate, dipentaerythrityl tributyratecaproate, dipentaerythrityl trivalerate trinonylate, dipentaerythrityl mixed hexaesters of C fatty acids and trimethylolpropane heptylate. Pentaerythritol esters of mixtures of C -C acids are excellent base oils, and are commercially available from Hercules Chemical Company.

Ester oils may be prepared by simple reaction of the alcoholic and acidic reactants in proportions suitable for producing the desired product; preparation preferably takes place in a solvent such as an aromatic hydrocarbon, and in the presence of a catalyst, such as HCl, HF, HBr, H 80 H PO SOC1 BF etc. Preparation of suitable esters is described in Eichemeyer, US. 3,038,859, issued June 12, 1962, and Young, U. S. 3,121,109, issued Feb. 11, 1964.

The lubricants of the invention may contain any other additives known to be beneficial in synthetic lubricants, such as additional extreme-pressure agents, thickeners, anti-lacquering agents, antifoam agents, dyes, and anticorrosion agents.

We claim as our invention:

1. A lubricant composition comprising a major amount of a synthetic ester base, 0.5 to by weight of a triaryl ester of phosphorothionic acid having 6 to 14 carbons per aryl group, and 0.5 to 5% by Weight of at least one member of the group consisting of diarylamines containing one to two rings per aryl group substituted with zero to four alkyl groups having one to ten carbon atoms and thiodiarylamines having a thiazine nucleus, said thiodiarylamines being substituted with zero to four alkyl groups having from one to ten carbon atoms.

2. A composition of claim 1 wherein the triaryl ester of phosphorothionic acid is triphenyl phosphorothionate.

3. A lubricant composition comprising a major amount of a synthetic ester base, 0.5% to 10% by weight of a triaryl ester of phosphorothionic acid having from six to fourteen carbons per aryl group, 0.5% to 5% by weight of a diarylamine having one to two rings per aryl group substituted with zero to four alkyl groups having from one to ten carbon atoms per alkyl group, and 0.5% to 5% by weight of a thiodiarylamine having a thiazine nucleus and having one to two rings per aryl group substituted with Zero to four alkyl groups having from one to ten carbon atoms.

4. The lubricant of claim 3 wherein the triaryl ester of phosphorothionic acid is triphenyl phosphorothionate.

5. The lubricant of claim 4 wherein the diarylamine is phenyl-a-naphthylamine.

6. The lubricant of claim 4 wherein the thiodiarylamine is selected from the group consisting of phenothiazine and 3,7-dioctyl phenothiazine.

7. A lubricant composition comprising a major amount of a synthetinc ester base, 0.5 to 10% by Weight of triphenyl phosphorothionate, 0.5 to 5% by weight of phenylu-naphthylamine, and 0.5 to 5% by Weight of 3,7-dioctyl phenothiazine.

8. A lubricant composition comprising a major amount of a synthetic ester base, 0.5 to 10% by weight of triphenyl phosphorothionate, 0.5 to 5% by weight of phenyla-naphthylamine, and 0.5 to 5% by weight of phenothiazine.

9. A lubricant composition consisting essentially of a major amount of a synthetic ester base lubricant, a minor stabilizing amount of a triaryl ester of phosphorothionic acid having 6 to 14 carbon atoms per aryl group and a minor amount of a diarylamine selected from the group consisting of diarylamines having one to two rings per aryl group, ring alkylated derivatives thereof, thiodiarylamine having a thiazine nucleus, and ring-alkylated derivatives thereof, said amine being present in an amount sufficient to enhance the oxidative stability imparted by said organophosphorus compound.

References Cited UNITED STATES PATENTS 2,242,260 5/1941 Prutton 252466 3,100,748 5/1963 Richards et a1. 25246.6 3,218,256 11/1965 Edwards et al 25247 DANIEL E. WYMAN, Primary Examiner.

W. H. CANNON, Assistant Examiner.

US. Cl. X.R. 

9. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR AMOUNT OF A SYNTHETIC ESTER BASE LUBRICANT, A MINOR STABILIZING AMOUNT OF A TRIARYL ESTER OF PHOSPHOROTHIONIC ACID HAVING 6 TO 14 CARBON ATOMS PER ARYL GROUP AND A MINOR AMOUNT OF A DIARYLAMINE SELECTED FROM THE GROUP CONSISTING OF DIARYLAMINES HAVING ONE TO TWO RINGS PER ARYL GROUP, RING ALKYLATED DERIVATIVES THEREOF, THIODIARYLAMINES HAVING A THIAZINE NUCLEUS, AND RING-ALKYLATED DERIVATIVES THEREOF, SAID AMINE BEING PRESENT IN AN AMOUNT SUFFICIENT TO ENHANCE THE OXIDATIVE STABILITY IMPARTED BY SAID ORGANOPHOSPHORUS COMPOUND. 